1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method.
2. Description of the Related Art
An office device such as an MFP (multi function printer) has been conventionally known to have an energy-saving standby mode in addition to a normal mode for normal operation. The energy-saving standby mode and the normal mode serve as operation modes of the device. In the energy-saving standby mode, the supply of power to any portions of the device is stopped during a time period such as nighttime in which the device is not used for long hours so that the power consumption of the device is reduced. For example, Japanese Patent Application Laid-open No. 2009-222824 discloses an image forming apparatus including a secondary battery in addition to an AC power source. This image forming apparatus has two operation modes that are a normal mode and an energy-saving standby mode. In the normal mode, electric power is supplied from the AC power source to each component of the image forming apparatus. In the energy-saving standby mode, on the other hand, the electric power is supplied from the secondary battery to each component of the image forming apparatus.
A lithium-ion secondary battery, which can be charged and discharged, has been widespread as a secondary battery used in electrical machinery and apparatus. The lithium-ion secondary battery has advantages such as a little memory effect phenomenon, a long cycle life, and a high electromotive force of 3.6 V for one battery. On the other hand, the lithium-ion secondary battery has disadvantages such as battery capacity deterioration caused by being used or stored in an almost fully charged state, and discharge capacity reduction due to repeated charge and discharge (ICHIMURA, Masahiro, Longevity Characteristics of Small Lithium-ion Battery, 3.2 Relationship between a discharge state in the partial discharge and cycle deterioration, NTT BTI 2005 [online], [retrieved on 2011-07-25]. Retrieved from the Internet: <URL:http://www.ntt-fsoken.co.jp/research/pdf.2005_ichi.pdf>.
If an MFP using a lithium-ion battery as a secondary battery does not use the power supplied from an AC power source and uses the power supplied only from the secondary battery in an energy-saving standby mode, the secondary battery needs to be charged during a normal mode so that the power charged in the second battery is not exhausted in the energy-saving standby mode. However, during business hours in which the MFP is often in operation, for example, switching between the normal mode and the energy-saving standby mode is frequently repeated. Such a repeating cycle constantly keeps the secondary battery in a highly charged state, causing a problem of accelerating secondary battery deterioration.
Therefore, there is a need for an image forming apparatus and an image forming method capable of reducing deterioration of a second battery and increasing longevity of the secondary battery.